|News, Reviews and Letters Index > Ace Review from Creative Computing Vol. 9, No. 7, July 1983|
The Jupiter Ace: a Forth computer.
By Christopher Helck.
No matter how you look at it, the Jupiter Ace, manufactured by Jupiter Contab Limited, is a small machine. Measuring 8-1/2" by 7-1/2" by 1-1/2", it is slightly larger than the Timex Sinclair. The price is also small. The machine is available by mail order for $150 from Computer Distribution Associates of Oxford, PA.
The most interesting thing about the Ace is that it comes with the Forth programming language in ROM. This means that when you turn the machine on, Forth, not Basic, is running. Because there is not much software currently available to run on this machine, those who buy it are buying an opportunity to learn to program in Forth, one of the up and coming microcomputer languages. A selection of games and programming tools is promised in the near future should you learn for other diversions once Forth is mastered.
Almost half of the surface of the Jupiter Ace is covered by its keyboard. The keyboard consists of sculpted rubber keys under which lies a flat keyboard. It is much easier to type on than the flat plastic membrane on the Timex and the Atari 400. That is not to say that it rivals the keyboard of a typewriter--the keys rock a little bit while you are typing. The space bar has become just another small key beneath the enter key, and a special symbol shift key is used to access punctuation. Overall, the keyboard has a nice feel, although those accustomed to full-sized keyboards will find it a bit cramped.
The computer itself is housed in a stylish white plastic case with red racing stripes and is a breeze to set up. It comes with an American plug adapter, a video cable with an RF modulator and two lines for hook-up to a cassette recorder. An ON/OFF switch would be a welcome addition. At the present time, to shut the machine off you must pull the plug.
The Ace is built around a Z80 microprocessor. It comes with 8K of ROM and 3K of RAM, expandable to 53K. The manufacturer promises to make 16K and 48K memory expansion modules available soon for $50 and $125 respectively. There are two card slots on the back. One is the Z80 pinout and the other is an edge connector that will support the memory expansion packs and an RS-232C interface when they become available.
The Ace is designed to be hooked up to a cassette recorder. A printer can also be added. The writers of the manual seem to be encouraging adventurous hardware designers to let their imaginations run wild and build exciting new peripherals. There is an example in the manual of how to hook up a traffic light controller. A built-in speaker allows beeps and even musical tones to be played. Forth And The Jupiter Ace Forth is an interpretive language which is gaining popularity. At its best, Forth is fast and compact; at its worst, it is unreadable. For numerical calculations, it uses reverse Polish notation--to add 3 to 2 enter 3 2 + rather than the more logical 3 + 2.
Instead of writing programs as in Basic, what you do on the Jupiter Ace is to write words in Forth. These words may then be used in other Forth words. For instance, once a square root function has been defined, it may be used anywhere, anytime, either in another word or interactively. As each word is defined in Forth, it is appended to the dictionary.
The Forth that comes with the Ace is a subset of Forth 79. The power of this small subset is a tribute to the strength of Forth. With the words included, an enterprising programmer could write a version of Basic if he so chose.
One or two additions to the standard vocabulary are worth mentioning. The Ace allows you to inspect and modify old words that have gotten buried within the dictionary without disturbing the words on top. In standard Forth, you would have to recompile the dictionary all over again.
The words IN and OUT are of potential interest to people like myself, who are intimidated by hardware and yet feel they should know something about it. IN and OUT allow you to read and write the input and output ports of the Z80. I haven't had the nerve to connect anything to the 80 pinout yet, but I am far more likely to do that than I would be to attach something to my IBM PC. Maybe I would even learn something.
The Ace version of Forth has its limitations as well as its advantages. The most important is that there are fewer than 1000 bytes of usable space to work with in the 3K version. This is not enough to write even a bad version of PAc-Man. In addition, the compiler is rather severe; it tends to wipe out the system when it runs into trouble. The main problem, however, seems to be in the user interface. After you type a line and hit ENTER, the computer tries to interpret the entire line, including the garbage to the right of the cursor (which is there because you did not bother to erase it when you backspaced) as a command. I found this very frustrating. On the other hand, the Ace does include a fairly nice line editor, and if you use it correctly, you won't have any garbage to the right of the cursor.
Related to this problem is the question, "Where is the input line?"
When the machine is brought up, the input line is at the bottom of the screen, which is where we come to expect it. However, certain commands move the input line about on the screen, leaving chaos in their wake.
Graphics On The Ace
The display is black and white. There are two display modes: a character mode, which provides 23 lines of 32 characters, and a graphics mode, which provides 46 lines of 64 pixels. The character set is defined in RAM, and it is amusing to play with it.
The only graphic command that the Ace supports is a point plotting routine; there are no line drawing commands built in. You can key in a Forth word, DRAW, for drawing lines. This command is described in the manual, along with a detailed explanation of how it works.
Overall, the manual is well written. It has some of the best beginner's explanations of some of the more difficult Forth words that I have seen anywhere. Everything it explains, it explains well.
In conclusion, the Jupiter Ace is a nicely designed but limited computer that is appropriate for people who want to learn to program in Forth. It is nice to have a computer that does what it is supposed to do--even if what it does is limited. Small can sometimes be beautiful.
Computer Distribution Associates, 53 South 3rd St., Oxford, PA 19363. (215) 932-4807.